Compared to charge-based memories, such as flash memories, passive resistive memory cells have a simpler design and can therefore be implemented on an ideal surface area of 4F2 at a given minimal feature size F. However, in a large array comprising many such memory cells, not only do currents flow through the above-mentioned memory cell, but there are also parasitic current paths through memory cells that have not been mentioned. This is a limiting factor for the maximum array size that can be implemented.
It is known from German patent 10 2009 023 153 to design a resistively switching memory element as an antiserial circuit that is composed of two memory cells. Each such memory element forms a high-resistance resistor, regardless of the state of the element (0 or 1), in parasitic current paths. The element is only briefly low-resistance when it is deliberately addressed while in state 1 and permeated by a read current. In this way, it is also possible to implement large arrays that are composed of many memory elements. This is achieved in exchange for the read-out of a 1 being destructive and the 1 having to be written back into the memory element after read-out.
German patent 10 2011 012 738 provides a method by way of which such memory elements can be read out non-destructively. The prerequisite for this is that the memory cells forming a memory element are manufactured differently, so that they can be distinguished from each other in a series connection via differing contributions to an electrical property of this series connection. The drawback is that this type of manufacture is technologically very complex and worsens the symmetry of the switching behavior of such memory elements.
It is the object of the invention to provide a method for read-out which is still non-destructive, but no longer dependent on two differently manufactured memory cells. It is a further object of the invention to provide memory elements that are in particular suitable for carrying out the method and, at the same time, technologically easy to produce.
These objects are achieved according to the invention by a method according to the main claim and by memory elements according to additional independent claims. Further advantageous embodiments will be apparent from the dependent claims.